build: Run docs and lint on py38

This requires moving some noqa comments due to 3.8's changes to the
ast module.

.travis.yml

@@ -34,9 +34,9 @@ jobs:
     - python: nightly
       env: TOX_ENV=py3-full
       # Docs and lint python versions must be synced with those in tox.ini
-    - python: '3.7'
+    - python: '3.8'
       env: TOX_ENV=docs
-    - python: '3.6'
+    - python: '3.8'
       env: TOX_ENV=lint
 
 install:

tornado/ioloop.py

@@ -233,13 +233,13 @@ def clear_instance() -> None:
     def current() -> "IOLoop":
         pass
 
-    @typing.overload  # noqa: F811
+    @typing.overload
     @staticmethod
-    def current(instance: bool = True) -> Optional["IOLoop"]:
+    def current(instance: bool = True) -> Optional["IOLoop"]:  # noqa: F811
         pass
 
-    @staticmethod  # noqa: F811
-    def current(instance: bool = True) -> Optional["IOLoop"]:
+    @staticmethod
+    def current(instance: bool = True) -> Optional["IOLoop"]:  # noqa: F811
         """Returns the current thread's `IOLoop`.
 
         If an `IOLoop` is currently running or has been marked as

tornado/web.py

@@ -424,14 +424,14 @@ def _convert_header_value(self, value: _HeaderTypes) -> str:
     def get_argument(self, name: str, default: str, strip: bool = True) -> str:
         pass
 
-    @overload  # noqa: F811
-    def get_argument(
+    @overload
+    def get_argument(  # noqa: F811
         self, name: str, default: _ArgDefaultMarker = _ARG_DEFAULT, strip: bool = True
     ) -> str:
         pass
 
-    @overload  # noqa: F811
-    def get_argument(
+    @overload
+    def get_argument(  # noqa: F811
         self, name: str, default: None, strip: bool = True
     ) -> Optional[str]:
         pass

tox.ini

@@ -40,8 +40,8 @@ basepython =
            # the outputs of the tools (especially where exactly the
            # linter warning-supression comments go), so we specify a
            # python version for these builds.
-           docs: python3.7
-           lint: python3.6
+           docs: python3.8
+           lint: python3.8
 
 deps =
      full: pycurl